The list of developmental events that may lead to intellectual disability in Down syndrome (DS) ranges from the over expression of single genes to altered synaptic and firing properties of neurons throughout the nervous system. Recently, our laboratory has discovered intrinsic defects in oligodendrocyte precursor cell (OPC) maturation that lead to changes in myelination and white matter tract formation in a mouse model of DS. This dysmyelination, confirmed using human brain gene expression profiling and myelin imaging, has been shown to lengthen the time it takes for action potentials to reach their postsynaptic targets. Since this novel cellular defect presumably underlies at least part of the intellectual disability in DS, a straightforward therapeutic approach would be to treat with compounds that promote OPC maturation. Initial results in mouse models look promising, but whether OPCs from humans with DS exhibit the same defects found in mouse model cells is critical for this effort. In this project, we will take advantage of pre-existing human stem cell lines and rapid OPC programming protocols to evaluate the maturation of human DS-derived OPCs for the first time. Next, in a series of in vitro experiments, we will test two FDA-approved drugs for their ability to prompt OPC differentiation and then test their myelination potential by transplanting these cells into the myelin-deficient Shiverer mouse brain. The results of these studies will generate a novel cellular resource for future study in the DS field, test the hypothesis that human DS-derived OPCs exhibit the same defects found in mouse model cells, and evaluate the efficacy of two potential drugs that could be used to improve myelination in the brains of people with DS.